Abstract:

Wireless communication terminals are disclosed that display the direction
and distance between them so that users can, for example, travel away
from each other and then later find one another. The terminals are
configured to track their movement using acceleration data. Some of the
terminals may operate as slave terminals in which they transmit their
movement data to a master terminal which determines therefrom the
relative direction and distance between the terminals. The master
terminal may then transmit the relative direction and distance data to
the slave terminals where it can be displayed to their users.

Claims:

1. A first wireless communication terminal comprising:a display device;a
wireless transceiver that is configured to communicate through an air
interface with a second wireless communication terminal;at least one
accelerometer that is configured to generate acceleration data responsive
to movement of the first terminal; anda controller that is configured to
generate movement data from the acceleration data that tracks movement of
the first terminal, to communicate the movement data to the second
terminal, to receive relative direction and distance data from the second
terminal, and to respond thereto by causing an indication of direction
and/or distance between the first and second terminals to be displayed on
the display device.

2. The first wireless communication terminal of claim 1, wherein the
controller is further configured to respond to activation of a terminal
tracking mode by causing an orientation pattern to be displayed.

3. The first wireless communication terminal of claim 2, further
comprising a plurality of light sources configured to generate a defined
orientation light pattern which indicates a present orientation of the
first terminal for use by the second terminal for determining relative
orientation between the first and second terminals, wherein the
controller is further configured to turn on the plurality of light
sources in response to activation of the terminal tracking mode.

4. The first wireless communication terminal of claim 3, wherein the
plurality of light sources are configured to emit light from spaced apart
asymmetrical peripheral locations on a same side of the first terminal to
generate an asymmetrical light pattern from the first terminal.

5. The first wireless communication terminal of claim 2, wherein the
controller is further configured to respond to activation of the terminal
tracking mode by causing a defined orientation pattern that indicates a
present orientation of the first terminal to be displayed on the display
device for use by the second terminal for determining relative
orientation between the first and second terminals.

6. The first wireless communication terminal of claim 1, wherein the
wireless transceiver comprises a wireless local area network (WLAN)
transceiver and a cellular transceiver, and the controller is further
configured to repetitively communicate the movement data to the second
terminal through the WLAN transceiver while a WLAN communication link to
the second terminal is available, and to respond to loss of the WLAN
communication link by repetitively generating discrete text messages
containing the movement data and communicating the text messages through
the cellular transceiver to the second terminal.

7. The first wireless communication terminal of claim 6, wherein the
controller is further configured to repetitively communicate the movement
data to the second terminal at a first repetition rate through the WLAN
transceiver while the WLAN communication link is available, and to
respond to loss of the WLAN communication link by repetitively generating
and communicating the text messages containing the movement data through
the cellular transceiver at a second repetition rate that is less than
the first repetition rate.

8. The first wireless communication terminal of claim 7, wherein the
controller is further configured to determine speed of the movement of
the first terminal, and to regulate the second repetition rate at which
the text messages containing the movement data are generated and
communicated in response to the determined speed.

9. The first wireless communication terminal of claim 1, wherein the
wireless transceiver comprises a wireless local area network (WLAN)
transceiver and a cellular transceiver, and the controller is further
configured to repetitively communicate the movement data to the second
terminal through the WLAN transceiver at a first repetition rate while a
WLAN communication link to the second terminal is available, and to
respond to loss of the WLAN communication link by generating a message
containing the movement data and communicate the message through the
cellular transceiver to the second terminal each time the first terminal
is determined to have moved at least a threshold distance from a location
of the previous communicated message containing the movement data.

10. A first wireless communication terminal comprising:a display device;a
wireless transceiver that is configured to communicate through an air
interface with a second wireless communication terminal;at least one
accelerometer that is configured to generate acceleration data responsive
to movement of the first terminal; anda controller that is configured to
generate movement data from the acceleration data that tracks movement of
the first terminal, to receive movement data from the second terminal
that tracks movement of the second terminal, to combine the movement data
for the first and second terminals to generate relative direction and
distance data between the first and second terminals, and to cause an
indication of direction and/or distance between the first and second
terminals to be displayed on the display device.

11. The first wireless communication terminal of claim 10, further
comprising an image sensor, wherein the controller is configured to
detect orientation of a defined pattern on the second terminal within
image data from the image sensor, and to determine relative orientation
between the first and second terminals responsive to the detected
orientation of the defined pattern on the second terminal.

12. The first wireless communication terminal of claim 11, wherein the
controller is configured to detect orientation of a light pattern emitted
by the second terminal within image data from the image sensor, and to
determine relative orientation between the first and second terminals
responsive to the detected orientation of the light pattern.

13. The first wireless communication terminal of claim 11, wherein the
controller is configured to detect orientation of a pattern displayed on
a display device of the second terminal within image data from the image
sensor, and to determine relative orientation between the first and
second terminals responsive to the detected orientation of the displayed
pattern on the second terminal.

14. The first wireless communication terminal of claim 10, wherein the
controller is further configured to transmit the relative direction and
distance data to the second terminal.

15. The first wireless communication terminal of claim 10, wherein the
wireless transceiver comprises a wireless local area network (WLAN)
transceiver and a cellular transceiver, and the controller is further
configured to repetitively communicate the relative direction and
distance data to the second terminal through the WLAN transceiver while a
WLAN communication link to the second terminal is available, and to
respond to loss of the WLAN communication link by repetitively generating
discrete text messages containing the relative direction and distance
data and communicating the text messages through the cellular transceiver
to the second terminal.

16. The first wireless communication terminal of claim 15, wherein the
controller is further configured to repetitively communicate the relative
direction and distance data to the second terminal at a first repetition
rate through the WLAN transceiver, and, in response to loss of the WLAN
communication link, to repetitively generate and communicate the text
messages containing the relative direction and distance data through the
cellular transceiver at a second repetition rate that is less than the
first repetition rate.

17. The first wireless communication terminal of claim 16, wherein the
controller is further configured to determine speed of the movement of
the first terminal, and to regulate the second repetition rate at which
the text messages containing the relative direction and distance data
communicated in response to the determined speed.

18. The first wireless communication terminal of claim 10, wherein the
controller is further configured to determine signal strength for a
received signal carrying the acceleration data from the second terminal,
to estimate distance between the first and second terminals in response
to a defined relationship between a known strength of the signal
transmitted by the second terminal and the received signal strength, and
to use the estimated distance to increase accuracy of the relative
direction and distance data that is generated using the movement data for
the first and second terminals.

19. A method comprising:at a first wireless communication terminal,
generating movement data from acceleration data that tracks movement of
the first terminal;at the first terminal, receiving movement data from a
second wireless communication terminal that tracks movement of the second
terminal;at the first terminal, combining the movement data for the first
and second terminals to generate relative direction and distance data
between the first and second terminals; anddisplaying at the first
terminal an indication of direction and/or distance between the first and
second terminals.

20. The method of claim 19, further comprising:detecting orientation of a
defined pattern on the second terminal within image data from an image
sensor in the first terminal;determining relative orientation between the
first and second terminals responsive to the detected orientation of the
defined pattern on the second terminal;repetitively communicating the
relative direction and distance data to the second terminal at a first
repetition rate through a WLAN transceiver in the first terminal while a
WLAN communication link to the second terminal is available, and
responding to loss of the WLAN communication link by repetitively
generating discrete text messages containing the relative direction and
distance data and communicating the text messages through a cellular
transceiver in the first terminal to the second terminal at a second
repetition rate that is less than the first repetition rate;
andregulating the second repetition rate at which the text messages
containing the relative direction and distance data are communicated in
response to speed of the movement of the first terminal and/or in
response to determining that the first terminal has moved at least a
threshold distance from a location of the previous communicated message
containing the movement data.

Description:

BACKGROUND OF THE INVENTION

[0001]The present invention relates to the field of wireless
communications in general and more particularly, to determining the
location of wireless communication terminals.

[0002]Many communication terminals, such as cellular communication
terminals, personal digital assistants (PDAs), laptop computers, and the
like, are now equipped with Global Positioning System (GPS) receivers to
enable users to determine their location. GPS is a space-based radio
triangulation system using a constellation of satellites in orbit around
the Earth. A GPS receiver triangulates its position based on timing of
radio signals it receives from various ones of the satellites and the
known location of those satellites.

[0003]Determining the position of a GPS receiver typically requires the
acquisition of a set of navigational parameters from the navigational
data signals of four or more GPS satellites. The algorithms that are used
to acquire GPS signals and determine position therefrom are complex and
require substantial processing throughput. The process of monitoring GPS
signals can be significantly affected by environmental factors. For
example, GPS signals that may be easily acquired in the open typically
become harder or impossible to acquire when a receiver is within a
building, a vehicle, and/or under foliage.

[0004]The process to acquire GPS signals can take several minutes
depending upon how much acquisition information a GPS receiver has
initially. In order to improve GPS receiver performance, techniques have
been developed to provide GPS receivers with GPS acquisition assistance
information, e.g., time and position estimates, satellite ephemeris and
clock information, and a visible satellite list from a terrestrial
cellular communication system, which can enable a GPS receiver to
expedite its acquisition of GPS signals and associated position
determination.

[0005]As can be appreciated, incorporating a GPS receiver and associated
processing circuitry into a wireless terminal can greatly increase its
cost and complexity. This cost and complexity further increases when the
wireless terminal is further configured to receive and use GPS
acquisition assistance information from a cellular communication system.

SUMMARY OF THE INVENTION

[0006]Various embodiments of the present invention provide wireless
communication terminals that display the direction and distance between
them so that users can, for example, travel away from each other and then
later find one another. The terminals are configured to track their
movement using acceleration data. Some of the terminals may operate as
slave terminals in which they transmit their movement data to a master
terminal which determines therefrom the relative direction and distance
between the terminals. The master terminal may then transmit the relative
direction and distance data to the slave terminals where it can be
displayed to their users.

[0007]According to some embodiments, a first wireless communication
terminal, which may correspond to a slave terminal, includes a display
device, a wireless transceiver, at least one accelerometer, and a
controller. The wireless transceiver is configured to communicate through
an air interface with a second wireless communication terminal. The at
least one accelerometer is configured to generate acceleration data
responsive to movement of the first terminal. The controller is
configured to generate movement data from the acceleration data that
tracks movement of the first terminal, to communicate the movement data
to the second terminal, to receive relative direction and distance data
from the second terminal, and to respond thereto by causing an indication
of direction and/or distance between the first and second terminals to be
displayed on the display device.

[0008]In some further embodiments, the controller is further configured to
respond to activation of a terminal tracking mode by causing an
orientation pattern to be displayed.

[0009]In some further embodiments, the first terminal can include a
plurality of light sources configured to generate a defined orientation
light pattern which indicates a present orientation of the first terminal
for use by the second terminal for determining relative orientation
between the first and second terminals. The controller can be further
configured to turn on the plurality of light sources in response to
activation of the terminal tracking mode.

[0010]In some further embodiments, the plurality of light sources are
configured to emit light from spaced apart asymmetrical peripheral
locations on a same side of the first terminal to generate an
asymmetrical light pattern from the first terminal.

[0011]In some further embodiments, the controller is further configured to
respond to activation of the terminal tracking mode by causing a defined
orientation pattern that indicates a present orientation of the first
terminal to be displayed on the display device for use by the second
terminal for determining relative orientation between the first and
second terminals.

[0012]In some further embodiments, the wireless transceiver includes a
wireless local area network (WLAN) transceiver and a cellular
transceiver. The controller is further configured to repetitively
communicate the movement data to the second terminal through the WLAN
transceiver while a WLAN communication link to the second terminal is
available, and to respond to loss of the WLAN communication link by
repetitively generating discrete text messages containing the movement
data and communicating the text messages through the cellular transceiver
to the second terminal.

[0013]In some further embodiments, the controller is further configured to
repetitively communicate the movement data to the second terminal at a
first repetition rate through the WLAN transceiver while the WLAN
communication link is available, and to respond to loss of the WLAN
communication link by repetitively generating and communicating the text
messages containing the movement data through the cellular transceiver at
a second repetition rate that is less than the first repetition rate.

[0014]In some further embodiments, the controller is further configured to
determine speed of the movement of the first terminal, and to regulate
the second repetition rate at which the text messages containing the
movement data are generated and communicated in response to the
determined speed.

[0015]In some further embodiments, the wireless transceiver includes a
wireless local area network (WLAN) transceiver and a cellular
transceiver, and the controller is further configured to repetitively
communicate the movement data to the second terminal through the WLAN
transceiver at a first repetition rate while a WLAN communication link to
the second terminal is available, and to respond to loss of the WLAN
communication link by generating a message containing the movement data
and communicating the message through the cellular transceiver to the
second terminal each time the first terminal is determined to have moved
at least a threshold distance from a location of the previous
communicated message containing the movement data.

[0016]In some other embodiments, a first wireless communication terminal,
which may correspond to a master terminal, includes a display device, a
wireless transceiver, at least one accelerometer, and a controller. The
wireless transceiver is configured to communicate through an air
interface with a second wireless communication terminal. The at least one
accelerometer is configured to generate acceleration data responsive to
movement of the first terminal. The controller is configured to generate
movement data from the acceleration data that tracks movement of the
first terminal, to receive movement data from the second terminal that
tracks movement of the second terminal, to combine the movement data for
the first and second terminals to generate relative direction and
distance data between the first and second terminals, and to cause an
indication of direction and/or distance between the first and second
terminals to be displayed on the display device.

[0017]In some further embodiments, the terminal further includes an image
sensor. The controller is configured to detect orientation of a defined
pattern on the second terminal within image data from the image sensor,
and to determine relative orientation between the first and second
terminals responsive to the detected orientation of the defined pattern
on the second terminal.

[0018]In some further embodiments, the controller is configured to detect
orientation of a light pattern emitted by the second terminal within
image data from the image sensor, and to determine relative orientation
between the first and second terminals responsive to the detected
orientation of the light pattern.

[0019]In some further embodiments, the controller is configured to detect
orientation of a pattern displayed on a display device of the second
terminal within image data from the image sensor, and to determine
relative orientation between the first and second terminals responsive to
the detected orientation of the displayed pattern on the second terminal.

[0020]In some further embodiments, the controller is further configured to
transmit the relative direction and distance data to the second terminal.

[0021]In some further embodiments, the wireless transceiver includes a
WLAN transceiver and a cellular transceiver, and the controller is
further configured to repetitively communicate the relative direction and
distance data to the second terminal through the WLAN transceiver while a
WLAN communication link to the second terminal is available, and to
respond to loss of the WLAN communication link by repetitively generating
discrete text messages containing the relative direction and distance
data and communicating the text messages through the cellular transceiver
to the second terminal.

[0022]In some further embodiments, the controller is further configured to
repetitively communicate the relative direction and distance data to the
second terminal at a first repetition rate through the WLAN transceiver,
and, in response to loss of the WLAN communication link, to repetitively
generate and communicate the text messages containing the relative
direction and distance data through the cellular transceiver at a second
repetition rate that is less than the first repetition rate.

[0023]In some further embodiments, the controller is further configured to
determine speed of the movement of the first terminal, and to regulate
the second repetition rate at which the text messages containing the
relative direction and distance data are communicated in response to the
determined speed.

[0024]In some further embodiments, the controller is further configured to
determine signal strength for a received signal carrying the acceleration
data from the second terminal, to estimate distance between the first and
second terminals in response to a defined relationship between a known
strength of the signal transmitted by the second terminal and the
received signal strength, and to use the estimated distance to increase
accuracy of the relative direction and distance data that is generated
using the movement data for the first and second terminals.

[0025]Some other embodiments are directed to a method that includes, at a
first wireless communication terminal, generating movement data from
acceleration data that tracks movement of the first terminal. Further, at
the first terminal, movement data is received from a second wireless
communication terminal that tracks movement of the second terminal.
Further, at the first terminal, the movement data for the first and
second terminals is combined to generate relative direction and distance
data between the first and second terminals. An indication of direction
and/or distance between the first and second terminals is displayed at
the first terminal.

[0026]In some further embodiments, the method further includes detecting
orientation of a defined pattern on the second terminal within image data
from an image sensor in the first terminal. The relative orientation
between the first and second terminals is determined responsive to the
detected orientation of the defined pattern on the second terminal. The
relative direction and distance data are repetitively communicated to the
second terminal at a first repetition rate through a WLAN transceiver in
the first terminal while a WLAN communication link to the second terminal
is available. In response to loss of the WLAN communication link,
discrete text messages containing the relative direction and distance
data are repetitively generated and communicated as text messages through
a cellular transceiver in the first terminal to the second terminal at a
second repetition rate that is less than the first repetition rate. The
second repetition rate at which the text messages containing the relative
direction and distance data are communicated is regulated in response to
speed of the movement of the first terminal and/or in response to
determining that the first terminal has moved at least a threshold
distance from a location of the previous communicated message containing
the movement data.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and constitute a
part of this application, illustrate certain embodiments of the
invention. In the drawings:

[0028]FIG. 1 illustrates a wireless communication terminal that is
operating in a tracking mode to sense orientation indicia on another
wireless communication terminal and determine therefrom the relative
orientation between the terminals in accordance with some embodiments of
the present invention;

[0029]FIG. 2 illustrates a wireless communication terminal that is
operating in a tracking mode and emits light from three light sources to
form an orientation light pattern that can be used by another wireless
communication terminal to determine the relative orientation there
between in accordance with some embodiments of the present invention;

[0030]FIG. 3 illustrates another wireless communication terminal that is
operating in a tracking mode and displays a defined orientation pattern
that indicates a present orientation of the terminal to another wireless
communication terminal in accordance with some embodiments of the present
invention;

[0031]FIG. 4 illustrates a pair of wireless communication terminals that
are operating in a tracking mode and which display directional arrows
that are dynamically updated to point toward one another in accordance
with some embodiments of the present invention;

[0032]FIG. 5 is a block diagram that illustrates a wireless communication
terminal that is configured to operate in a tracking mode in accordance
with some embodiments of the invention;

[0033]FIG. 6 is a flowchart and data flow diagram showing exemplary
operations of a pair of wireless communication terminals that
cooperatively determine the relative direction and distance between the
terminals using acceleration data in accordance with some embodiments of
the invention; and

[0034]FIG. 7 is a flowchart that illustrates operations within a wireless
communication terminal for transmitting movement data selectively through
a short range transceiver or a cellular transceiver, and for regulating a
repetition rate of the data transmissions in accordance with various
embodiments of the invention.

DETAILED DESCRIPTION

[0035]Various embodiments of the present invention will now be described
more fully hereinafter with reference to the accompanying drawings.
However, this invention should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are provided so
that this disclosure will be thorough and complete, and will convey the
scope of the invention to those skilled in the art.

[0036]It will be understood that, as used herein, the term "comprising" or
"comprises" is open-ended, and includes one or more stated elements,
steps and/or functions without precluding one or more unstated elements,
steps and/or functions. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. The term "and/or" and "/" includes
any and all combinations of one or more of the associated listed items.
In the drawings, the size and relative sizes of regions may be
exaggerated for clarity. Like numbers refer to like elements throughout.

[0037]Some embodiments may be embodied in hardware and/or in software
(including firmware, resident software, micro-code, etc.). Consequently,
as used herein, the term "signal" may take the form of a continuous
waveform and/or discrete value(s), such as digital value(s) in a memory
or register. Furthermore, various embodiments may take the form of a
computer program product on a computer-usable or computer-readable
storage medium having computer-usable or computer-readable program code
embodied in the medium for use by or in connection with an instruction
execution system. Accordingly, as used herein, the terms "circuit" and
"controller" may take the form of digital circuitry, such as
computer-readable program code executed by an instruction processing
device(s) (e.g., general purpose microprocessor and/or digital signal
processor), and/or analog circuitry.

[0038]Embodiments are described below with reference to block diagrams and
operational flow charts. It is to be understood that the functions/acts
noted in the blocks may occur out of the order noted in the operational
illustrations. For example, two blocks shown in succession may in fact be
executed substantially concurrently or the blocks may sometimes be
executed in the reverse order, depending upon the functionality/acts
involved. Although some of the diagrams include arrows on communication
paths to show a primary direction of communication, it is to be
understood that communication may occur in the opposite direction to the
depicted arrows.

[0039]As used herein, a "wireless communication terminal" or abbreviated
"terminal" includes, but is not limited to, any electronic device that is
configured to transmit/receive communication signals with a long range
wireless interface such as, for example, a cellular interface, and/or via
a short range wireless interface such as, for example, a Bluetooth
wireless interface, a wireless local area network (WLAN) interface such
as IEEE 801.11a-g, and/or another radio frequency (RF) interface. Example
terminals include, but are not limited to, a cellular phone, PDA, and
mobile computers that are configured to communicate with another terminal
via a cellular network and/or over a Bluetooth interface, WLAN interface,
and/or another RF interface.

[0040]In accordance with various embodiments of the present invention, two
or more terminals display the direction and distance between them so that
users can, for example, travel away from each other and then later find
one another. The terminals are configured to track their movement using
acceleration data. Some of the terminals may operate as slave terminals
in which they transmit their movement data to a master terminal which
determines therefrom the relative direction and distance between the
terminals. The master terminal then transmits the relative direction and
distance data to the slave terminals where it is displayed to their
users.

[0041]Accordingly, the master terminal is configured with algorithms and
processing capabilities to determine the relative direction and distance
between the master terminal and one or more slave terminals and to
display the relative direction and distance to a user, and may be further
configured to communicate the relative direction and distance data to the
slave terminals. In sharp contrast, the slave terminals can have
substantially less circuitry complexity than the master terminal and may,
for example, be configured to transmit their individual movement data to
the master terminal and not have a display, receiver circuitry, and other
circuitry for determining, receiving, or displaying relative direction
and distance to the master terminal. Accordingly, a slave terminal may be
a relatively simple and inexpensive movement tracking device with a
wireless transmitter. In some other embodiments described below, a slave
terminal can receive the relative direction and distance data from a
master terminal and can display that data to enable a user thereof to
navigate to the master terminal.

[0042]FIG. 1 illustrates a first wireless communication terminal 100 and a
second wireless communication terminal 120 that are operating in a
tracking mode. In response to a user commanding the first and second
terminals 100 and 120 to activate the tracking mode, an alignment
initialization process causes a display device 102 in the first terminal
100 to display a message (e.g., "where are you?") that confirms
activation of the tracking mode and indicates to the user that the
relative positions and directional orientation of the first and second
terminals 100 and 120 need to be initialized.

[0043]To initialize their relative positions and directional orientation,
the first and second terminals 100 and 120 may be brought into close
proximity to one another in a predefined relative orientation, and at
which time a user can trigger initialization of an initial distance and
orientation between the first and second terminals 100 and 120. Movement
from that location can then be tracked using acceleration data. For
example, the first and second terminals 100 and 120 can be stacked on one
another and oriented so that their respective top and bottom surfaces are
aligned, and a user can press a button on the first/second terminal
100/120 to trigger initialization. Alternatively, as will be described
below, the first terminal 100 can use an image sensor to sense and use
the initial orientation between the first and second terminals 100 and
120.

[0044]Referring to FIG. 1, the first and second terminals 100 and 120 can
be brought into close proximity to one another. The second terminal 120
generates a defined orientation light pattern which indicates a present
orientation of the second terminal 120 (e.g., indicates a direction of
the top of the terminal). FIG. 2 illustrates a closer view of the second
terminal 120 which includes three light sources 122, 124, and 126 (e.g.,
light emitting diodes) that are spaced apart asymmetrically along
peripheral locations on a same side of the second terminal 120. In
response to entering an alignment initialization process of the terminal
tracking mode, the light sources 122, 124, and 126 are turned-on to
generate an orientation light pattern which is sensed by the first
terminal 100 and used to determine a relative orientation between the
first and second terminals 100 and 120.

[0045]The first terminal 100 includes an image sensor, such as a camera,
and is configured to detect, within image data from the image sensor, the
orientation of the light pattern generated by the second terminal 120.
The first terminal 100 uses the orientation of the detected light pattern
to determine the initial relative orientation (e.g., relative directional
angle) between the first and second terminals 100 and 120. In the present
example, the first terminal 100 detects that the first and second
terminals 100 and 120 are pointed in nearly opposite directions at some
determined angle. The terminal 100 determines the initial relative
orientation between the terminals 100 and 120 from the detected
orientation light pattern, and tracks its movement (including rotational
and distance movement) relative to that initial relative orientation. By
configuring the first terminal 100 to automatically detect the relative
orientation between the first and second terminals 100 and 120, the
directional and distance determinations that are carried out during the
tracking mode may be less prone to user error (e.g., user misalignment of
the terminals during orientation initialization) and may result in the
users' perceiving the tracking mode as being less complex to use.

[0046]It is to be understood that although the second terminal 120 has
been illustrated with three light sources spaced apart along peripheral
locations, the invention is not limited thereto and may instead include
any number of light sources or other detectable characteristic (e.g.,
color differences/shading markings on the terminal housing) that can be
used by the first terminal 100 to determine a present orientation of the
second terminal 120 relative to the first terminal 100.

[0047]For example, the second terminal 120 shown in FIG. 3 displays a
directional arrow that is always pointed toward a top surface of the
second terminal 120 during the alignment initialization process. The
first terminal 100 can sense and use the directional arrow displayed on
the second terminal 120 to determine the initial relative orientation
between the first and second terminals 100 and 120.

[0048]After initializing the relative orientation, the first and second
terminals 100 and 120 can be moved therefrom while cooperatively sharing
movement data, which is generated using accelerometer data, to track the
distance and direction between the first and second terminals 100 and
120. Persons can therefore use the tracking mode of the first and second
terminals 100 and 120 to travel away from each other and then later find
one another.

[0049]In the exemplary embodiment shown in FIG. 4, the first and second
terminals 100 and 120 display directional arrows that respectively point
toward the other terminal and which are dynamically updated as one or
both of the terminals 100 and 120 are moved. One or both of the terminals
100 and 120 may also display an indication of the distance between the
first and second terminals 100 and 120. The distance may be displayed as
a numerical value and/or it may be graphically indicated by scaling the
size of and/or varying the color of the displayed directional arrows
and/or other indicia that are displayed on one or both of the first and
second terminals 100 and 120. The displayed distance and direction may be
rendered so as to indicate to the operators the two-dimensional or
three-dimensional distance and direction between the terminals 100 and
120. For example, the directional arrows may rotate clockwise and
counterclockwise as the terminals 100 and 120 move around one another,
and may further rotate upward and downward and/or change to different
defined colors as the terminals 100 and 120 move upward and downward
relative to one another (e.g., when one terminal moves to a building
floor above or below the other terminal).

[0050]For example, the first and second terminals 100 and 120 may
increase/decrease the displayed size of the directional arrows and/or
increase/decrease the size of an icon that represents the other terminal
as the first and second terminals 100 and 120 are moved closer together
and, correspondingly, decrease/increase the displayed size of the indicia
as the first and second terminals 100 and 120 are moved further apart.

[0051]FIG. 5 is a block diagram that illustrates an exemplary embodiment
of the terminal 100. Referring to FIG. 5, the terminal 100 can include a
plurality of transceivers, such as a Bluetooth transceiver 112, a WLAN
transceiver 114 (e.g., compliant with one or more of the IEEE 801.11a-g
standards), and a cellular transceiver 116.

[0053]The first terminal 100 can thereby communicate with a similarly
configured second terminal 120 over short ranges, which may be less than
about 100 meters when using a WLAN communication link through the WLAN
transceiver 114 or less than about 10 meters when using a Bluetooth
communication link through the Bluetooth transceiver 112. The first
terminal can further communicate with the second terminal 120 over much
greater ranges using the cellular transceiver 116 communicating through
one or more cellular transceiver base stations 150.

[0054]The transceivers 112, 114, and 116 typically include both a
transmitter and a receiver to allow bi-directional communications, but
the present invention is not limited to such transceivers and, as used
herein, a "transceiver" may include only a receiver or a transmitter
pursuant to various embodiments described herein.

[0055]A multi-axis accelerometer module 118 can include a plurality of
accelerometer sensors that are arranged to measure acceleration and
rotation along a plurality of orthogonal axes, such as along the
illustrated horizontal axes Hx and Hy and the vertical axis Hz. A camera
122 or other image sensor generates image data that can be used to detect
an orientation light pattern or other indicia on the second terminal 120
and to determine therefrom the initial orientation between the first and
second terminals 100 and 120. A display 124 is configured to display an
indication of the direction and distance to the second terminal 120, such
by controlling the illustrated arrow to pointing toward the second
terminal 120 (represented by the displayed graphical icon) and a
numerical value for the distance (e.g. "20 m").

[0056]The terminal 100 may further include a speaker 126, a microphone
128, and a user input interface 130. An electronic compass 132 may be
provided that generates directional data that can be used to track
rotation of the terminal 100 and which may be combined with the
accelerometer data to improve tracking of movement of the terminal 100. A
controller 140 is configured to integrate the functionality of the other
components and to carry out one or more operations described herein for
tracking movement of the terminal 100 and for determining and displaying
the relative direction and distance between the first and second
terminals 100 and 120.

[0057]The controller 140 is configured to integrate acceleration data from
the accelerometer module 118 over time (e.g., double integration over
time) to determine the distance and direction that the terminal 100 has
moved from the initialized location. The controller 140 may further
combine directional data from the electronic compass 132 with the
acceleration data to increase the accuracy with which it tracks the
terminal's movement. The controller 140 receives movement data from the
second terminal 120, and combines that movement data with its internally
generated movement data to determine and display the relative distance
and direction between the first and second terminals 100 and 120. As will
be described further below, the controller 140 can further transmit the
determined relative direction and distance to the second terminal 120 for
display thereon so that a person can similarly use the second terminal
122 to navigate toward the first terminal 100.

[0058]In some further embodiments, the controller 140 may measure the
distance between the first and second terminals 100 and 120 in response
to the strength of wireless signals that are received from the second
terminal 120. The controller 140 may estimate the distance using a
defined relationship between an expected strength of the signal
transmitted by the second terminal 120 and the strength of the signal
that is received by first terminal 100. For example, a Bluetooth
transceiver and/or a WLAN transceiver within the second terminal 120 can
be expected to transmit with a relatively constant signal strength.
Accordingly, a relationship can be defined by which the controller 140
can determine the distance between the first and second terminals 100 and
120 in response to the expected strength of the second terminal's
transmitted signal and the strength of the signal that is received by the
Bluetooth transceiver 112 and/or the WLAN transceiver 114. Based on the
transmission pattern and associated gain of the transmitting antenna and
the receiving antenna, the transmitted and received signal strength may
be related by the distance squared or the distance cubed. The distance
that is measured based on received signal strength can be combined with
the movement data that is generated in response to the acceleration data
to improve the accuracy with which the distance and direction are
determined between the first and second terminals 100 and 120.

[0059]FIG. 6 is a flowchart and data flow diagram showing exemplary
operations 600 that can be carried out by the first and second terminals
100 and 120 while they are operating in a tracking mode to cooperatively
determine the relative direction and distance between them. Referring to
FIG. 6, in response to a user activating a tracking mode (operation 602),
the first terminal 100 transmits a signal (operation 604) to the second
terminal 120 to activate its tracking mode. The second terminal 120
responds thereto by displaying (operation 608) a query to a user to
authorize initiation of the tracking mode and, responsive to the user's
authorization, displaying an orientation pattern, such as the exemplary
asymmetric light pattern 122-126 shown in FIG. 2.

[0060]The first terminal 100 identifies (operation 606) the orientation
pattern on the second terminal 120 within the image stream from the
camera 122. The first terminal 100 determines (operation 610) the
relative orientation between the first and second terminals 100 and 120.
The relative orientation can correspond to one or more angles that are
determined between one or more defined axes through first and second
terminals 100 and 120. The first terminal 100 transmits the relative
orientation data (operation 612) to the second terminal 120.

[0061]The first terminal 100 displays (operation 614) on the display 124
an indication of the initial direction and distance to the second
terminal 120. The second terminal 120 may similarly display (operation
616) an indication of the initial direction and distance to the first
terminal 100.

[0062]The first terminal 100 then tracks its movement (operation 618)
using acceleration data from the multi-axis accelerometer module 118. The
second terminal 120 similarly tracks its movement (operation 630) using
acceleration data from an accelerometer module, and further transmits
(operation 632) its movement data to the first terminal 100.

[0063]The acceleration data that is transmitted from the second terminal
120 to the first terminal 100 may include raw acceleration data from the
accelerometer module. Alternatively, the second terminal 120 may
integrate the raw acceleration data over time to generate data that
indicates an accumulated distance traveled by the second terminal 120
over an elapsed time and may transmit that distance data to the first
terminal 100. By transmitting accumulated distance data instead of raw
acceleration data, the bandwidth that is used to communicate the movement
data to the first terminal 100 can be substantially decreased without
substantially affecting the accuracy with which the first terminal 100
tracks the movement of the second terminal 120.

[0064]The first terminal 100 combines (operation 620) its movement data
with the movement data that is received from the second terminal 120 to
determine the present direction and distance between the first and second
terminals 100 and 120. As described above, the first terminal 100 may
further estimate the distance between the first and second terminals 100
and 120 based on strength of a signal that is received from the second
terminal 120, such as the strength of the signal received from the second
terminal 120 that carries the movement data. The first terminal 100 can
combine the distance estimate that is based on the received signal
strength with the distance that is determined based on acceleration data
to improve the accuracy with which the distance between the first and
second terminals 100 and 120 is determined.

[0065]The first terminal 100 can transmit (operation 622) to the second
terminal 120 the data that indicates the relative direction and distance
between the first and second terminals 100 and 120. The first terminal
100 displays (operation 624) on the display 124 an indication of the
direction and the distance from the first terminal 100 to the second
terminal 120. The second terminal 120 can similarly display (operation
634) on a display an indication of the direction and the distance from
the second terminal 120 to the first terminal 100.

[0066]While the tracking mode is active, the first terminal 100 can
continue to repeat the operations 618 through 624 (illustrated by
collective operation 626) to dynamically determine the direction and
distance from the first terminal 100 to the second terminal 120 as one or
both of the terminals moves. The second terminal 120 can similarly repeat
operations 630 through 636 (illustrated by collective operation 636)
while the tracking mode is active to dynamically track and report its
movements to the first terminal 100 and to display the relative direction
and distance from the second terminal 120 to the first terminal 100.

[0067]Thus, by way of example, two users can quickly initialize the
tracking mode by operating one of the terminals to take a picture of
other terminal, thereby allowing automated detection of the relative
orientation of the terminals. The users can then proceed to separately
wander around a store, a theme park, or another venue while the terminals
track their movements and while the users are presented with an
indication of the direction and distance to one another. The users may
thereby easily use their respective terminals to navigate back to one
another. Because the terminals can track movement using acceleration data
from the accelerometers, instead of using GPS signals and GPS receiver
circuitry and positioning algorithms, the associated movement tracking
circuitry can be less complex and, therefore, less expensive.

[0068]Moreover, because the terminals can communicate with one another
through a short-range interface, such as a WLAN communication link, they
may selectively operate independent of a cellular or other subscriber
network and thereby avoid incurring added operational costs for the
users. When the terminals communicate with one another through a
long-range interface, such as through a cellular network, the terminals
may be configured to selectively reduce the amount of data traffic that
is communicated between the terminals so as to reduce the potential costs
that are incurred by the users. Exemplary operations that may be carried
out by the first terminal 100 and/or the second terminal 122 to
selectively reduce the amount of data traffic that is communicated
between the terminals while tracking movement are described below with
regard to FIG. 7.

[0069]FIG. 7 is a flowchart that illustrates operations 700 that can be
carried out within the first terminal 100 and/or the second terminal 120
for transmitting movement data selectively through a WLAN/Bluetooth
transceiver or a cellular transceiver based on availability of a
WLAN/Bluetooth communication link, and for regulating a repetition rate
of the data transmissions in accordance with various embodiments of the
invention. For purposes of explanation only, the operations 700 are
described below in the context of being carried out by the second
terminal 120.

[0070]Referring to FIG. 7, the second terminal 120 establishes (operation
702) a WLAN/Bluetooth communication link with the first terminal 100. The
second terminal 120 repetitively transmits (operation 704) its movement
data to the first terminal 100 at a first repetition rate through the
WLAN/Bluetooth communication link while the WLAN/Bluetooth communication
link is present. In response to losing the WLAN/Bluetooth communication
link (determined at operation 706), the second terminal 120 determines
(operation 708) whether cellular service is available and whether it
knows a messaging address of the first terminal 100. When cellular
service is available and it knows a messaging address for the first
terminal 100, the second terminal 120 begins transmitting its movement
data through discrete text messages to the first terminal 100 through a
cellular communication link at a second repetition rate that is less than
the first repetition rate. Alternatively or additionally, the second
terminal 120 can transmit its movement data through text messages to the
first terminal 100 through the cellular communication link in response to
determining that the second terminal has moved at least a threshold
distance from a location where it last transmitted its movement data
through a text message.

[0071]Although the transmission of the movement data through the
WLAN/Bluetooth communication link is typically free to the users, such
transmission through the cellular system generally incurs associated
costs to the users. To reduce these costs, the second terminal 120
controls the second repetition rate so as to reduce the number of text
messages that are used to communicate the movement data to the first
terminal 100 through the cellular system. Accordingly, the second
terminal 120 may communicate the movement data less frequently and/or may
wait until it determines it is moved at least a threshold distance before
it transmits new movement data to the first terminal 100 while it is
communicating movement data through text messages via the cellular
system.

[0072]Moreover, the second terminal 120 may determine its speed of
movement and may vary (operation 712) the second repetition rate in
response to the determined speed. Thus, while the second terminal 120 is
moving at a relatively slow speed (e.g., below a first threshold speed),
it may transmit it movement data less frequently through text messages,
and may corresponding increase the frequency of its transmission through
text messages when it is moving at a relative higher speed (e.g., above a
second threshold speed).

[0073]The second terminal 120 can continue to search (operation 714) for
the availability of the WLAN/Bluetooth communication link to the first
terminal 100, and when it becomes available again, may reestablish
(operation 702) a WLAN/Bluetooth communication link with the first
terminal 100. While the tracking mode is active (determined at operation
716) and the WLAN/Bluetooth communication link is not available, the
second terminal 120 may continue to repeat operations 710 through 716.

[0074]In the drawings and specification, there have been disclosed
embodiments of the invention and, although specific terms are employed,
they are used in a generic and descriptive sense only and not for
purposes of limitation, the scope of the invention being set forth in the
following claims.